If you decide to empty the trash in OS X, and end up getting an error or otherwise not seeing the contents delete (it happens many times), first try holding the Option key when emptying, which will invoke the OS X Force Empty feature, bypassing things like file locks and removing any file you have in the Trash.
If such behavior happens for files on a locally attached drive, you can go about fixing the issue by locating and removing the hidden trash folders (one in your account, and the other at the root of each locally mounted volume on the system), so the system will rebuild it with proper access permissions the next time you place an item in the trash.
So, open the Terminal (in the Applications > Utilities folder) and copy/paste these two lines, one line at a time, to the Terminal, but since they recursively target specific folders, be sure to use this exact syntax to avoid any problems:
sudo rm -rf ~/.Trash sudo rm -rf /Volumes/*/.Trashes
These two commands will be the quickest way to clear and rebuild the trash folders on your Mac.
Do not be intimidated by the Terminal, it is the best geek tool to control your computer.